1. Field of the Invention
The present invention relates generally to electromagnetic energy radiation and reception, and especially relates to electromagnetic energy radiation and reception effected using impulse radio energy. Still more particularly the present invention provides an antenna that exhibits a generally continuous signal response between a first frequency and a second frequency and further exhibits a deviation from the signal response substantially at a selected frequency between the first frequency and the second frequency.
2. Related Art
Recent advances in communications technology have enabled an emerging, revolutionary ultra wideband technology (UWB) called impulse radio communications systems (hereinafter called impulse radio).
Impulse radio was first fully described in a series of patents, including U.S. Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989), U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990) and U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton. A second generation of impulse radio patents includes U.S. Pat. No. 5,677,927 (issued Oct. 14, 1997) to Fullerton et al; and U.S. Pat. No. 5,687,169 (issued Nov. 11, 1997) and U.S. Pat. No. 5,832,035 (issued Nov. 3, 1998) to Fullerton. These patent documents are incorporated herein by reference.
Uses of impulse radio systems are described in U.S. patent application Ser. No. 09/332,502, entitled, xe2x80x9cSystem and Method for Intrusion Detection Using a Time Domain Radar Array,xe2x80x9d and U.S. patent application Ser. No. 09/332,503, entitled, xe2x80x9cWide Area Time Domain Radar Array,xe2x80x9d both filed Jun. 14, 1999, both of which are assigned to the assignee of the present invention, and both of which are incorporated herein by reference.
Basic impulse radio transmitters emit short pulses approaching a Gaussian monocycle with tightly controlled pulse-to-pulse intervals. Impulse radio systems typically use pulse position modulation, which is a form of time modulation where the value of each instantaneous sample of a modulating signal is caused to modulate the position of a pulse in time.
For impulse radio communications, the pulse-to-pulse interval is varied on a pulse-by-pulse basis by two components: an information component and a pseudo-random code component. Unlike direct sequence spread spectrum systems, the pseudo-random code for impulse radio communications is not necessary for energy spreading because the monocycle pulses themselves have an inherently wide bandwidth. Instead, the pseudo-random code of an impulse radio system is used for channelization, energy smoothing in the frequency domain and for interference suppression.
Generally speaking, an impulse radio receiver is a direct conversion receiver with a cross correlator front end. The front end coherently converts an electromagnetic pulse train of monocycle pulses to a baseband signal in a single stage. The data rate of the impulse radio transmission is typically a fraction of the periodic timing signal used as a time base. Because each data bit modulates the time position of many pulses of the periodic timing signal, this yields a modulated, coded timing signal that comprises a train of identically shaped pulses for each single data bit. The impulse radio receiver integrates multiple pulses to recover the transmitted information.
Antennas having ultra-wide band (UWB) properties are desired for a variety of applications, including impulse radio applications for communications, positioning, and other uses. Historically the principal use of UWB antennas has been in multi-band communication systems. Such multi-band communication systems require an ultra-wide band antenna that can handle narrow band signals at a variety of frequencies.
The recently emerging impulse radio communications technology often referred to as impulse radio has placed different, more stringent requirements on antenna performance. Impulse radio communication uses UWB signals, so an antenna for use in an impulse radio system must transmit or receive (or, transmit and receive) over all frequencies across an ultra-wide band at the same time. Thus, ultra-wide band impulse radio requires that an antenna performs well over ultra-wide bandwidths, and is also non-dispersive of those signals.
One solution applied to meeting the increasing commercial demand for multi-band systems has been to combine a variety of different narrow band operational modes in one antenna device. For example, a mobile phone may be provided with an antenna apparatus that can operate with cellular phone frequencies around 850 MHz, as well as operate with PCS (personal communication service) frequencies around 1900 MHz. For economic and cosmetic reasons (such as compact size), it is desirable that a multi-band device be provided with a single antenna that can function at potentially widely separated narrow bands of interest.
Widespread deployment of ultra wideband or xe2x80x9cUWBxe2x80x9d systems that use wide expanses of bandwidth in their operation, leaves the systems and apparatuses using such UWB antennas vulnerable to whatever narrowband sources of interference might co-exist in a given environment.
A variety of techniques have been used to create multi-band antennas in the past. One technique uses a tuned antenna that relies on a variable reactance, such as a variable capacitor or variable inductance, to create a resonance for making the antenna effective over a particular narrow band of interest. Even with the advent of more sophisticated micro-electro-mechanical systems (MEMS), such tuned antennas require a potentially complicated, expensive, and bulky tuning system that may not be commercially optimal.
Another technique has involved creating a single antenna that is responsive to multiple narrow bands of interest. Such an antenna is commonly constructed as a composite structure of narrow band resonant antenna sections that can operate in their respective corresponding narrow bands of interest.
An exemplary such prior art composite multi-band antenna may, for example, include an assembly of a variety of narrowband structures, such as a low band structure having a spectral response that is resonant around a first center frequency fA, a mid-band structure having a spectral response that is resonant around a second center frequency fC, and a high-band structure having a spectral response that is resonant around a third center frequency fE. The respective center frequencies fA, fC, fE are established according to the relationship:
fA less than fC less than fE 
Such a composite multi-band antenna has a spectral response that is resonant at a low frequency fA, at a mid frequency fC, and at a high frequency fE. Such a composite multi-band antenna is preferably designed to be nonresponsive at a first boundary frequency fB between fA and fC and to be nonresponsive at a second boundary frequency fD between fC and fE. Use of terms like xe2x80x9clow,xe2x80x9d xe2x80x9cmid,xe2x80x9d and xe2x80x9chigh,xe2x80x9d are for illustrative purposes only and should not be construed as referring to any particular range of frequencies. Similarly, although the hypothetical composite multi-band antenna is described as being responsive to three narrow bands, this does not preclude the present discussion from pertaining to dual band antennas, nor to antennas responsive to four or more bands.
The approach described above relating to constructing a composite antenna structure for establishing operational responsiveness in a plurality of narrow bands delineated by nonresponsive boundary frequencies within a wide band of frequencies is fraught with difficulties and disadvantages. Although the respective narrowband resonant structures may individually be quite responsive to their particular narrowband resonant frequencies of interest, when the various narrow band structures are combined together to form a composite multi-band antenna the performance of the respective narrowband resonant structures will inevitably degrade. Mutual coupling may be introduced between or among respective narrowband resonant structures that can cause spurious and undesired modes of operation as well as limit the performance of the desired modes of operation. Harmonic signals may be generated and various signals may interfere with each other to cancel or reinforce each other, all contributing to the degradation of integrity in effecting signaling. To some extent, such mutual coupling and interaction can be compensated for by methods known in the art involving combinations of filtering or amplifiers or other compensating circuitry. Radio frequency (RF) absorbing materials or shielding structures may also be employed in seeking to limit unwanted interaction of signals. In general, however, overall performance of such a composite multi-band antenna will suffer relative to the performance achievable from respective resonant component structures individually operating at their particular narrowband resonant frequencies of interest (e.g., fA, fC, fE). A composite multi-band antenna is a case in which the whole is less than the sum of its parts.
Attempts have been made to create ultra wideband (UWB) antenna systems that are insensitive to particular frequencies. Such a frequency selective, or frequency-rejecting, UWB antenna system typically included a UWB antenna element connected via a transmission line to a frequency filter. In a typical example, a UWB antenna element has a frequency response sensitive across an ultra wideband range of frequencies from a first frequency fA to a second frequency fE that is higher than first frequency fA. A frequency filter is provided for passing an ultra wideband range of frequencies from fA to fE with the exception of those frequencies in the vicinity of frequencies at which interference is to be avoided, such as a first intermediate frequency fB (between frequencies fA, fC) and a second intermediate frequency fD (between frequencies fC, fE). The frequency filter may be embodied in a discrete component filter, in a composite transmission line resonant filter, or in another RF filtering means known in the art. The resulting spectral response of such a frequency selective UWB antenna system is sensitive to an ultra wideband range of frequencies from fA to fE with the exception of frequencies in the vicinity of fB and fD. Frequencies in the vicinity of fB and fD are xe2x80x9crejectedxe2x80x9d from the overall spectral response. That is, the antenna is significantly less responsive to signals at rejection frequencies fB and fD than to signals at other frequencies. Such a frequency selective UWB antenna system may be coupled via an output interface to an appropriate transmitter, receiver, or transceiver.
Whether an antenna structure is constructed for establishing operational responsiveness in a plurality of narrow bands within a wide band of frequencies or is constructed as a frequency selective UWB antenna system to attain similar operational characteristics, the overriding problems associated with prior art approaches result in bulky, complex and inefficient antenna structures.
It is desirable to have a UWB antenna system that is selectively insensitive to one or more narrow bands of interest. Such selective insensitivity may be advantageously established in order to avoid interference with certain particular frequencies within the UWB operating range of the antenna. For example, frequency rejection may be arranged to avoid interference with global positioning system (GPS) equipment or cellular telephone equipment. Preferably, a UWB antenna system is embodied in a single UWB antenna with a frequency sensitive response offering multi-band narrowband coverage, as well as an ultra wideband response with significantly lesser sensitivity of response to signals within particular narrow rejection frequency bands. In general, performance of a UWB system deteriorates with increasing number of rejection frequency bands, but a system designer may be able to accept one or perhaps two rejection frequency bands as part of an overall compatibility and interference strategy.
There is a need for a small ultra wideband antenna that is simple in construction yet can be made less responsive to signals within particular rejection frequency bands. In particular, there is a need for a small, simply constructed ultra wideband antenna that is efficient in operation as well as frequency selective.
An electromagnetic antenna apparatus exhibits a generally continuous signal response between a first frequency and a second frequency, and further exhibits a deviation from the signal response in a frequency region centered substantially at a selected frequency between the first frequency and the second frequency. The apparatus includes: (a) an antenna transceiving element; (b) a feed structure coupled with the antenna receiving element for communicating transceiving signals with the antenna transceiving element; and (c) a discontinuity structure in the antenna transceiving element coupled with the feed structure. The discontinuity structure is configured for effecting return of selected transceiving signals to the feed structure as return signals. The return signals effect the deviation.
It is therefore an object of the present invention to provide an electromagnetic antenna apparatus that exhibits a generally continuous signal response between a first frequency and a second frequency, that further exhibits a deviation from the signal response in a frequency region centered substantially at a selected frequency between the first frequency and the second frequency, and that is small, simply constructed and efficient in operation.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.